Hyperbranched polymers (HBPs) have attracted significant attention because of their characteristic topological structure associated with their unique physical properties compared with those of the corresponding linear polymers. Dendrimers are the most structurally controlled HBPs, but the necessity of a stepwise synthesis significantly limits their applications in materials science. Several methods have been developed to synthesize HBPs by a one-step procedure, as exemplified by the use of AB2 monomers and AB′ inimers under condensation and self-condensing vinyl polymerization conditions. However, none of these methods provides structurally controlled HBPs over the three-dimensional (3D) structure, i.e., molecular weight, dispersity, number of branching points, branching density, and chain-end functionalities, except under special conditions. Here, we introduce a monomer design concept involving two functional groups with hierarchical reactivity and demonstrate the controlled synthesis of dendritic HBPs over the 3D structure by the copolymerization of the designed monomer and acrylates under living radical polymerization conditions.
Dendritic highly branched polystyrenes (HB-PSts) were prepared by ao ne-step copolymerization of dienyl telluride 6 and St in the presence of organotellurium chain transfer agent 2.T he molecular weight (MW), dendritic generation, and branching density were easily controlled by the ratio of 2 to 6 to styrene (St) with maintaining monodispersity.The branching efficiency estimated by adeuteriumlabeling experiment showed that 6 quantitatively (> 95 %) served as the branching point. The end group fidelity was high (ca. 90 %) as determined by the end group transformation to pyrene-derivative.I ntrinsic viscosity of the HP-polystyrenes was significantly lower than that of linear polystyrenes and were easily tuned by the branching number and branching density.The method is compatible of various functional groups and chloro and acetoxy-substituted styrenes were also used as ac omonomer.Atadpole blockc opolymer was also synthesized starting from linear PSt as amacroinitiator.Highly branched polymers (HBPs) have attracted ag reat deal of attention owing to their unique topological structure associated with characteristic physical properties,s uch as alower intrinsic viscosity,lower glass transition temperature, and alarger number of terminal groups than the corresponding linear polymers. [1] Therefore,H BPs are promising for various applications including lubricants,c oatings,d rugdelivery vehicles,a nd catalysts. [2] However,t he development of ap ractical method for synthesizing structurally controlled HBPs has been asignificant challenge.Among HBPs,d endrimers and dendrons are the most precisely controlled three-dimensional (3D) structures,t hat is,m olecular weight, dispersity,b ranching number, and branching density.H owever, the necessity of am ultistep synthesis limits their applications in materials science. [3] In contrast, hyperbranched polymers can be easily synthesized by one-step methods,s uch as 1) the step-growth polycondensation of AB n monomers and the copolymerization of A 2 and B n monomers,i nw hich Aa nd Br efer to two functional groups that react with each other and nrepresents the numbers of Bg roups, [4] and 2) self-condensing vinyl (co)polymerization (SCV(C)P) and self-condensing ringopening polymerization using the AB* monomer,i nw hich
The controlled synthesis of highly branched (HB) poly(methyl methacrylate) (PMMA) with a molecular weight of up to 88 × 10 3 gmol and low dispersity (Ð < 2.0) was achieved by the radical copolymerization of vinyltelluride, H 2 C=CHTePh (4cD), and MMA in the presence of the organotellurium chain transfer agent 6cI at 30 °C. Control of the branching structure was suggested by the Mark-Hauwink-Khun-Sakurada plots corresponding to samples in solution and trapped ion mobility spectroscopy-time of flight mass spectrometry in the gas phase. The mechanism of 4cD for the structural control of HB-PMMA synthesis comes from the hierarchical reactivity of the C-Te bond of 4cD, which serves as the branching point only after 4cD reacts and is incorporated into the polymer chain. In contrast, copolymerization using previously reported vinyltellurides 4aA (H 2 C=C(Me)TeMe) and 4aB (H 2 C=C(Me)-CH=CHTeMe) could not control the branching structure due to the b-carbon fragmentation reaction from the intermediate radicals generated from 4aA and 4bB. The theoretical calculations suggest that the suppression of the undesired fragmentation reaction when using 4cD is due to the acceleration of the desired propagation reaction forming a branched structure instead of decelerating the fragmentation reaction. Due to the versatility of radical polymerization, methacrylates with bulky substituents, such as t-butyl methacrylate, and polar functional groups, such as N,N-dimethylethyl methacrylate (DMAEM), were also used as monomers to afford structurally controlled corresponding HB polymers. These studies clearly open a new possibility for the use of HB polymers in macromolecular engineering.File list (2) download file view on ChemRxiv HB-PMMA_final.pdf (0.98 MiB) download file view on ChemRxiv HB-PMMA-SI_final.pdf (1.77 MiB)
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